All oil is not created equal

NPR recently spoke about how oil is not created equal. There are differing types of oil, with some having higher sulpher content as well as other parameters making it easier or harder to refine into the higher quality fuels.

http://www.npr.org/2011/02/25/134056647/ripple-in-libyan-oil-markets-make-waves-worldwide

"It happens that Libyan crude has almost no sulfur and produces a great deal of diesel fuel per barrel of crude, which means it is very valued," he says. "One can think of it as fat-free milk."
Libyan oil is light and sweet — it's the kind that refineries want for making low-sulfur diesel, which is widely desired in Europe, and jet fuel, of which the U.S. makes a lot. Both markets require low-sulfur fuel because it pollutes less.

It's a short (<4 minute) introduction to some of the intricacies of the energy markets and I suggest you listen to it.